1. Field of the Invention
This invention relates to bearings for rotary cone rock bits.
More particularly, this invention relates to synthetic diamond bearings for rotary cone rock bits. These diamond bearings may take the form of axial, radial or conical bearings and do not require conventional lubricants and attendant seals to function in an earth formation to form a borehole therein.
2. Description of the Prior Art
Diamond material has not been readily used to form bearings between two rotating parts. This is particularly true in roller cone rock bits. U.S. Pat. No. 4,190,301 teaches an axial thrust bearing for a roller drill bit comprising a pair of opposed diamonds. One diamond is mounted in the axial end face of the journal bearing and the other is mounted in the interior of the cutting roller supported for rotation on the journal. Each diamond is mounted on a cup shaped casing made of a softer metal than the journal and cutting roller. This patent differs from the present invention in that it is a single point bearing as opposed to an enlarged curved bearing surface covered with diamond material.
U.S. Pat. No. 4,260,203, entitled "Bearing Structure for a Rotary Rock Bit", is assigned to the same assignee as a present invention. A rotary rock bit is disclosed having bearing surfaces which have extremely long wear resistant properties. The rock bit comprises a plurality of legs extending downwardly from the bit body with cutter cones rotatively mounted on journals cantilevered from each leg of the bit body. One or more engaging bearing surfaces formed between the cone and the journal include a layer of diamond material mounted on a substrate of carbide. In one embodiment the bearing material forms the thrust button adjacent to the spindle located at the end of the journal. In another embodiment the bearing material is located on the inner engaging axial faces of the journal and the cone. In still another embodiment the bearing material is a segmented cylindrical bearing located in a circumferential groove formed in the journal.
While this patent generally teaches the use of diamond material for a bearing it does not specifically point out how the bearing is fabricated between all of the inner engaging rotating surfaces.
U.S. Pat. No. 4,345,798 teaches a means to reduce wear of contacting bearing surfaces. Anti-friction devices or bearings with diamond-containing concretion in the bearing surfaces are lapped before they are used for bearings.
This patent, however, does not teach the use of a multiplicity of small cubical diamond segments strategically placed on a surface to form a bearing.
U.S. Pat. No. 4,468,138 teaches diamond bearings consisting of a supporting plate/ring having a plurality of recesses equally spaced therearound with insert members consisting of hardmetal or carbide studs with planar faces of polycrystalline diamond positioned thereon. The diamond bearing faces are made co-planar by placing soft meltable metal pads in the bottom of each recess before insertion of the bearing studs. The assembly is placed with the bearing faces down on a smooth planar support, followed by heating the assembly to a temperature at which the metal pads melt thus allowing the metal pads to extrude around the base of each insert and thereby brazing the bearing inserts in place. When the assembly has cooled, the bearing inserts have their diamond bearing faces locked in co-planar relation by the extruding metal from the metal pads.
This patent basically teaches a method to mount tungsten carbide studs faced with diamond bearing material within recesses and provides a means to align a diamond bearing surface so that it is co-planar with an adjacent diamond bearing surface.
Finally, U.S. Pat. No. 4,560,014, assigned to the same assignee as the present invention, teaches a bidirectional thrust bearing assembly used between a downhole fluid motor and a rock bit for drilling oil wells. The bearing assembly has a stationary housing with radial journal bearing sleeves and a rotatable driving shaft, also having radial bearing sleeves. A pair of oppositely facing thrust bearing rings are mounted in the housing. A second pair of thrust bearing rings are mounted on the shaft so as to have faces opposing the bearing faces on the first pair of rings. Belleville springs resiliently bias a pair of thrust bearing rings apart and carry the thrust load between such rings. Each ring has a plurality of inserts of hard material, preferably polycrystalline diamond, at the bearing surface. Means are provided for circulating drilling fluid from the motor to the thrust bearing faces forming hydrodynamic fluid bearing films in the bearing faces.
This patent provides a pair of radial thrust bearings that are biased against each other with an intermediate series of Belleville springs. Like the foregoing patent, the diamond bearing package includes a series of polycrystalline diamond studs equidistantly spaced around the circumference of the bearing ring. The patent does not teach the use of a multiplicity of small flat cubic diamond segments bonded to a bearing surface to provide a bearing material.
A number of patents describe the use of hardmetal material for bearings such as rods or buttons. For example, tungsten carbide flush type buttons have been used to provide a bearing surface. The buttons are mounted circumferentially in the same fashion as the foregoing patents '138 and '014. The following U. S. Pat. Nos. 3,879,094, 4,029,368 and 4,549,820, utilize hardmetal tungsten carbide buttons or rods for bearings. U.S. Pat. Nos. 3,879,094 and 4,029,368 are both assigned to the same assignee as the present invention.
None of the foregoing patents teach the use a multiplicity of strategically placed, small, flattened, cubical diamond segments bonded or mounted to the surface of a bearing. A multiplicity of small segments are secured within a matrix to form a bearing that is relatively large in area.
The present invention has a distinct advantage over the foregoing prior art patents by providing a means to utilize diamond material on a bearing surface regardless of the curvature of the surface. Diamonds generally of the same size, with any geometry, may be utilized for a particular bearing application provided at least one surface is flat. For example, natural or synthetic diamond segments may be shaped as triangles, cubes, tetrahedrons or spheres as long as at least one bearing surface is substantially flat. By using small cubical diamond particles and orienting their flats along the curved or flat surface of the bearing, greater surface area can be realized, thus providing more bearing surface; as opposed to utilizing large, circular, widely separated polycrystalline diamond discs mounted within, for example, tungsten carbide substrates.